The present invention relates to a hammer device, preferably a down-the-hole hammer, including a casing, a piston, a drill bit and means for activating the piston to frequently strike the drill bit. The invention also relates to a piston and a drill bit per se.
In down-the-hole hammers the kinetic energy of the piston is transmitted by elastic waves through the drill bit and finally to the rock. However, said transmission is not carried out in an optimal way since the piston is not related to the drill bit in terms of length and mass. Also the drill bit does not cooperate with the rock in the best mode.
In prior art down-the-hole hammers very little attention has been paid to the adaptation of the piston to the drill bit when said drill bit has a mass concentration at the end directed towards the rock.
In applicants U.S. Pat. No. 5,305,841, however, the importance of choosing appropriate impedance on the cooperating drill bit and piston, is discussed. The document discloses a down-the-hole hammer, wherein the drill bit includes front and rear portions of different impedance, and the piston includes front and rear portions of different impedance. In the drill bit, the front portion has a larger impedance than the rear portion. In the piston, the rear portion has a larger impedance than the front portion. However the rear portion of the drill bit and the front portion of the piston include relatively small masses, which negatively affects the degree of efficiency during drilling. Furthermore, the known hammer device has been complicated to manufacture due to the requirements for guiding the elongated portions of the bit and the piston.
The objects of the present invention are to further improve the energy transmission from the piston to the rock via the drill bit and to facilitate the manufacture of the hammer device. This is realized by paying attention also to the distribution of the impedance in the piston and the drill bit of a hammer device as defined in the appending claims.